1. Field of the Invention
This invention relates to display devices and more particularly, to electrochromic display devices using non-aqueous electrolytic systems of styryl-like compounds or dyes of a specific type which exhibit electrochromic behavior.
2. Description of the Prior Art
Electrochromic display devices making use of styryl-like compounds have been described in U.S. Pat. No. 4,003,633, issued to Akio Yamashita, in which the styryl-like compounds are dissolved in a liquid crystal and a color development is based on a principle that the solution is oriented by application of an electric field. By the application, a steric effect is produced on the styryl compound whereupon the ring of the compound is opened, resulting in generation of color. When the electric field is removed, the orientation of the liquid crystal is disturbed and the styryl-like compound restores its original ring-closed colorless structure. However, this color-generating system is relatively low in electrochromic efficiency. In order to increase such an efficiency, surface active agents such as dodecylpyridinium chloride, cetylpyridinium bromide or the like, stabilizing agents such as p-benzoquinone and/or electron-donating materials such as HCl, pyridinium salts, ammonium salts are added to the liquid crystal solution.